unwanted random sharpness/smoothness,
This happens because of blenders shading methods when you use a subsurface modifier 

the loop cuts are so close together , so blender can't figure out how to shade it 

a simple solution is to use less details (Loop cuts) and a better topology (Loop cuts that follows the bending of the car surface here)

so here it should going from one side and bending in a V shape to the other.
Also you don't need to use that much loop cuts. Instead depend on the subsurface modifier to create more detail 

something like this





Note : I added the double close edges to make the edges appear sharper 

I recommend the anvil tutorial of blender guru on YouTube he goes more on depth on this